Production method for aluminium alloys

ABSTRACT

A production method for aluminium alloys includes an addition process of adding into a molten aluminium alloy a precipitation nucleus on which an intermetallic compound is capable of precipitating when the molten aluminium alloy is solidifying and a casting process of casting the molten aluminium alloy containing the precipitation nucleus into a metal mold. The molten aluminium alloy contains a high density of nuclei consisting of the precipitation nuclei separated from a liquid phase of the molten aluminium alloy and initially nucleated nuclei from the liquid phase of the molten aluminium alloy.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under 35 U.S.C. § 119 of Japanese patent application No. 2018-108580 filed on Jun. 6, 2018, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a production method of aluminium alloys.

DESCRIPTION OF THE RELATED ART

There is an known production method for aluminium alloys with which fine crystal grains are produced by having intermetallic compounds nucleate in a molten aluminium alloy (For example, see JP2004-202899A and JP2000-319741A). The aluminium alloy produced with this production method has excellent mechanical properties such as a high fracture strength, a high elongation, a high fatigue strength and excellent workability (moldability).

If such an aluminium alloy production method as above mentioned is applied to production of a reused aluminium alloy ingot produced of a scrapped aluminium alloy material, it is possible to produce the reused aluminium ingot with 3% of the energy to be consumed for producing a virgin aluminium alloy ingot through smelting the aluminium alloy material. In addition, the aluminium alloy as produced with this production method has fine crystal grains as is mentioned and a fracture strength 50% higher than such a general aluminium alloy as ADC12.

SUMMARY OF THE INVENTION

However, if such a conventional production method as explained in JP2004-202899A or JP2000-319741A is used, there is a risk that intermetallic compounds included in the aluminium alloy become larger than needed. These enlarged intermetallic compounds can be origins for the fracture of the aluminium alloy and deteriorate significantly the workability (moldability). Furthermore, in the case of the scrapped aluminium alloy that contains more Fe than the virgin material, the intermetallic compounds are much more likely to become larger.

Considering the above mentioned problems, the present invention has an objective to provide a production method for aluminium alloys containing fine intermetallic compounds.

In order to achieve the objective above mentioned, the aluminium alloy production method of the present invention comprises an addition process of adding into a molten aluminium alloy precipitation nuclei on which intermetallic compounds are capable of precipitating when the molten aluminium alloy is solidifying and a casting process of casting into a metal mold the molten aluminium alloy containing the precipitation nuclei.

The present invention enables providing an aluminium alloy production method with which an aluminium alloy containing fine intermetallic compounds is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an aluminium alloy production method of a practised example of the present invention.

FIG. 1B illustrates an aluminium alloy production method of a comparison example.

FIG. 2 shows dependence of the size of the intermetallic compounds on a temperature keeping time in the temperature keeping process of the production method of a practised example of the present invention.

FIG. 3A is a reflected electron image photograph taken with a scanning electron microscope of an aluminium alloy raw material used as a raw material in a practised example of the present invention.

FIG. 3B is a reflected electron image photograph taken with a scanning electron microscope of an aluminium alloy produced through a production method of a practised example of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Next, an aluminium alloy production method of an embodiment of the present invention is explained.

The production method of this embodiment comprises an addition process in which precipitation nuclei from which intermetallic compounds are to precipitate when a molten aluminium alloy is solidifying are added into the molten aluminium alloy, a temperature keeping process in which the molten aluminium alloy containing the precipitation nuclei is kept at a predetermined temperature for a predetermined time and a casting process in which the molten aluminium alloy containing the precipitation nuclei is cast into a metal mold.

<Addition Process>

The molten aluminium alloy into which precipitation nuclei are added is explained.

(Molten Aluminium Alloy)

The molten aluminium alloy into which the precipitation nuclei are added contains Si, Fe, Cu, Mg and Zn.

[Si: 6.5˜8.5 Mass %]

A Si content should be between 6.5˜8.5 mass %, which results in the resultant aluminium alloy having a higher stiffness, an improved wear resistant property and a smaller thermal expansion coefficient. In addition, since the Si content is equal to or more than 6.5 mass %, the resultant aluminium alloy has a liquid phase line lowering with the Si content increasing, which results in easier melting of raw materials and easier casting of the aluminium alloy.

[Fe: 0˜0.9 Mass %]

A Fe content should be between 0˜0.9 mass %, which results in the resultant aluminium alloy having a higher stiffness, an improved wear resistant property and a smaller thermal expansion coefficient.

[Cu: 0.15˜0.35 Mass %]

A Cu content should be between 0.15˜0.35 mass %, which results in the resultant aluminium alloy having an improved mechanical strength at elevated temperatures and a smaller thermal expansion coefficient.

[Mg: 0.25˜0.45 Mass %]

A Mg content should be 0.25˜0.45 mass %, which results in the resultant aluminium alloy having a higher strength. In addition, since the Mg content is equal to or less than 4.5 mass %, the resultant aluminium alloy maintains a sufficiently high fracture toughness.

[Zn: 0.3˜0.6 Mass %]

A Zn content should be 0.3˜0.6 mass %, which results in the resultant aluminium alloy having an improved strength.

[Al and Unavoidable Impurities: Remainder]

The remainder of the molten aluminium alloy excluding Si, Fe, Cu, Mg and Zn consists of Al and unavoidable impurities.

In addition, it is preferable to add Mn and Be into the molten aluminium alloy before the precipitation nuclei are added.

Adding Mn has an effect of making an intermetallic compound of Al, Fe and Si in a particle shape when the molten aluminium alloy is solidifying. It is preferable to add an amount of Mn that is equal to 60% of an amount of Fe in the molten aluminium alloy.

Adding Be has an effect of inhibiting oxidation of the molten aluminium alloy, especially inhibiting reduction of Mg due to its oxidation. In addition, Be has an effect of making an intermetallic compound of Al, Fe and Si in a particle shape when the molten aluminium alloy is solidifying. An amount of Be to be added is 0.01˜0.1 mass % to the molten aluminium alloy.

<Precipitation Nucleus>

Precipitation nuclei to be added into the molten aluminium alloy may be selected to be what has a good crystal matching property with the intermetallic compounds that precipitate when the molten aluminium alloy is solidifying.

An amount of the precipitation nuclei to be added may be from 1 tenth to one third of the mass of the molten aluminium alloy.

Such precipitation nuclei as are fit to be added into the molten aluminium alloy should be selected based on a disregistry factor δ and one example is the intermetallic compound as has been mentioned.

[Precipitation Nuclei Selected Based on Disregistry Factor]

The precipitation nuclei selected based on the disregistry factor δ are such as having a disregistry factor δ that is defined by the following Bremfitt equation and is equal to or lower than 10%.

δ_((hkl)n) ^((hkl)s)=1/3Σ_(i=1) ³ |d[uvw]_(s) ^(i) cos θ−d[uvw]_(n) ^(i) |/d[uvw]_(n) ^(i)×100 [%]

where, (hkl)_(s) refers to a low-order index face of a different nucleus particle, [uvw]_(s) refers to a low-order index direction of the (hkl)_(s) face, (hkl)_(n) refers to a low-order index face of a metal whose nuclei are generated, [uvw]_(n) refers to a low-order index direction of the (hkl)_(n) face, d [uvw]_(s) refers to a distance between atoms in the [uvw]s direction, d [uvw]_(n) refers to a distance between atoms in the [uvw]_(n) direction, and θ refers to an angle between [uvw]_(s) and [uvw]_(n).

The precipitation nuclei to be selected in this way are, for example, VC, TiC, TiB₂, AlB₂, ZrC, NbC and W₂C, although not limited to these. Among these precipitation nuclei, TiC is preferable.

[Intermetallic Compounds]

Intermetallic compounds selected for the precipitation nuclei are, for example, intermetallic compounds of MgSi system, AlFe system, AlMn system, AlNi system, AlCu System, AlFeSi system, AlFeMn system, AlFeMnSi system, AlFeMnSiCr system, AlFeNi system, AlMnNi system, AlFeMnNi system, AlCr system, AlTi system, AlZr system or AlFeNi system, although not limited to these. Among these intermetallic compounds, Fe system intermetallic compounds are preferable and AlFeSi system intermetallic compounds are especially preferable. One or more of these intermetallic compounds are selected and used for the precipitation nuclei.

<Temperature Keeping Process>

In the temperature keeping process of the production process of the present embodiment, the molten aluminium alloy containing the precipitation nuclei selected in the way above mentioned is kept at a predetermined temperature for a predetermined duration.

The predetermined temperature at which the molten aluminium alloy is kept in this embodiment may be a temperature to which the temperature of the molten aluminium alloy is cooled and at which initially precipitated nuclei should nucleate in the molten aluminium alloy.

The predetermined duration for which the molten aluminium alloy is kept in this embodiment may be appropriately determined and may be several tens of seconds or around 1 minute, although not limited to this duration.

When the initially precipitated nuclei nucleate in the molten aluminium alloy during the temperature keeping process, the density of precipitation nuclei in the molten aluminium alloy with the added precipitation nuclei present becomes significantly higher.

Since the molten aluminium alloy is kept at the predetermined temperature for the predetermined duration, the size of the precipitation nuclei are fine, which is explained below.

<Casting Process>

The molten aluminium alloy after the temperature keeping process is cast into a metal mold in the casting process of the present embodiment.

Intermetallic compounds grow on the increased nuclei consisting of the added precipitation nuclei and the initially precipitated nuclei in the molten aluminium alloy in the metal mold. When this growth gets under way, the intermetallic compounds precipitate simultaneously on so many nuclei that the intermetallic compounds become fine in the aluminium alloy produced after the molten aluminium alloy solidifies. In addition, the smaller nuclei produced during the temperature keeping process also contributes to the resultant fine intermetallic compounds in the resultant aluminium alloy.

<Action/Effect>

Next, Actions and effects of the production method for aluminium alloys of the present embodiment are explained.

Since precipitation nuclei of the intermetallic compounds are added into the molten aluminium alloy, the intermetallic compounds are fine in the aluminium alloy that is obtained after the molten aluminium alloy solidifies.

The resultant aluminium alloy has excellent mechanical properties of the fracture strength, the elongation and the fatigue strength and excellent workability.

In addition, since the production method of the present embodiment has the temperature keeping process in which the molten aluminium alloy is kept at the predetermined temperature, the size of the nuclei from which the intermetallic compounds precipitate is made smaller, which ensures that the resultant aluminium alloy includes fine intermetallic compounds.

In addition, the production method of the present embodiment has the addition process in which Be and Mn as well as the precipitation nuclei are added into the molten aluminium alloy containing Fe. As a result, the intermetallic compounds in the solidified aluminium alloy have a particle shape, which results in the intermetallic compounds being made further finer. Moreover, the production method of this embodiment has an effect of inhibiting oxidation of elements contained in the aluminium alloy.

The production method of the present embodiment makes use of the precipitation nuclei whose disregistry factor δ according to Bramfitt equation is equal to or less than 10%, which results in further ensuring that the intermetallic compounds in the aluminium alloy are made fine.

The production method of the present embodiment makes use of the precipitation nuclei of the predetermined intermetallic compounds, which results in further ensuring that the intermetallic compounds in the aluminium alloy are made fine.

The production method of the present embodiment utilizes the precipitation nuclei of an AlFeSi system intermetallic compound or TiC, which results in further ensuring that the intermetallic compounds in the aluminium alloy are made fine.

The embodiments of the present invention are not limited to those which have been explained and can be modified within the technical scope of the present invention. The explained embodiment of the present invention uses the molten aluminium alloy containing Si, Fe, Cu, Mg and Zn. However the present invention is not limited to the embodiments using the molten aluminium alloy containing these elements and the embodiments of the present invention may use the molten aluminium alloy containing such elements as are contained in known aluminium alloy as well. The molten aluminium alloy of the embodiment does not necessarily contain all of these elements and may contain predetermined amounts of at least those elements of which known intermetallic compounds can precipitate.

PRACTISED EXAMPLE

Next the present invention is further specifically explained comparing a production method for aluminium alloys of the present invention with a production method for aluminium alloys of a comparison example. FIG. 1A illustrates an aluminium alloy production method of a practised example of the present invention and FIG. 1B illustrates an aluminium alloy production method of a comparison example.

Practised Example 1

<Addition Process>

As is shown in FIG. 1A, precipitation nuclei 2 (Solid phase S) were added into the molten aluminium alloy 1 of a liquid phase L before the aluminium alloy 1 started to be cooled in the addition process of the production method of the practised example.

The molten aluminium alloy 1 was produced by heating and melting a raw material of an aluminium alloy which consists of 10 mass % Si, 1 mass % Fe and a remainder of Al and less than 0.1 mass % of unavoidable impurities. The precipitation nuclei 2 including α-AlFeSi was used.

The temperature of the molten aluminium alloy was 720° C. An amount of the precipitation nuclei 2 added into the molten aluminium alloy 1 was one third of a mass of the molten aluminium alloy. The temperature of the precipitation nuclei 2 was 500° C. when they were added.

<Temperature Keeping Process>

As is shown in FIG. 1A, the molten aluminium alloy 1 of the liquid phase L was gradually cooled to 590° C. in the temperature keeping process of the production method of this practised example 1. Initially precipitated nuclei 3 nucleated in the molten aluminium alloy 3 while the temperature of the molten aluminium alloy 1 was lowering. Accordingly there is a high density of nuclei in the molten aluminium alloy 1, including precipitation nuclei 2 that are separated into the molten aluminium alloy 1 (Liquid phase L) from the solid phase S and initially precipitated nuclei 3 that nucleated from the liquid phase L of the molten aluminium alloy.

In the production method of this practised example, the nucleation of the initially precipitated nuclei as above explained took place when the molten aluminium alloy is kept at the predetermined keeping temperature for the predetermined keeping time.

As explained, initially precipitated nuclei nucleate in the molten aluminium alloy while the temperature of the molten aluminium alloy is lowering. In the temperature keeping process of this practised example, the molten aluminium alloy may be kept, for example, at a temperature at which initially precipitated nuclei can nucleate for a predetermined keeping time. There is a certain correlation between this temperature keeping time and the size of intermetallic compounds in the aluminium alloy obtained after the molten aluminium alloy solidifies.

FIG. 2 is a graph illustrating the relation between the temperature keeping time [sec] and the size of intermetallic compounds [μm].

As is shown in FIG. 2, the size of intermetallic compounds [μm] gradually decreases to a local minimum as the keeping time [sec] increases from 0 [sec]. As the temperature keeping time [sec] further increases, the size of intermetallic compounds [μm] increases from the local minimum.

In the present practised example, a preferable range (t1˜t2) of the temperature keeping time [sec] is determined to be a range within which the size of intermetallic compounds [μm] is determined to be smaller. Specifically, the preferable temperature keeping time [sec] for the predetermined keeping temperature of 590° C. was determined to be within a range from 20 sec to 30 sec.

<Casting Process>

Next, the casting process of casting the molten aluminium alloy 1 after the temperature keeping process as indicated in FIG. 1A into a metal mold (not shown) was carried out.

Intermetallic compounds precipitated and grew from the increased nuclei (of added precipitation nuclei 2 and initially precipitated nuclei 3) in the molten aluminium alloy in the metal mold. When the precipitation and the growth of the intermetallic compounds 4 got started, intermetallic compounds 4 started to precipitate almost simultaneously on the increased nuclei in the molten aluminium alloy. As a result, the aluminium alloy 5 obtained after the molten aluminium alloy 1 after solidified contained fine intermetallic compounds 4. Furthermore, since the nuclei that nucleate during the temperature keeping process have a smaller size, the intermetallic compounds 4 in the aluminium alloy 5 are certainly made fine. The intermetallic compounds 4 in the aluminium alloy 5 obtained through the temperature keeping process are 23% smaller than those in the aluminium alloy without the temperature keeping process performed.

FIG. 3A is a reflected electron image photograph (whose magnification is 200) taken with a scanning electron microscope (SEM) of a raw material used for the aluminium alloy 1 in a practised example of the present invention. FIG. 3B is a reflected electron image photograph (whose magnification is 200) taken with a scanning electron microscope (SEM) of the aluminium alloy 5 produced through a production method of a practised example of the present invention.

As shown in FIG. 3B, it turns out that the intermetallic compounds 4 in the aluminium alloy 5 produced through the production method are siginificanly smaller than the intermetallic compounds in the aluminium alloy raw material as shown in FIG. 3A.

Practised Example 2

<Addition Process>

In this practised example, an Al—TiC alloy of a solid phase S was added into the molten aluminium alloy 1 of a liquid L in the addition process as shown in FIG. 1A before cooling the molten aluminium alloy 1 got started.

The molten aluminium alloy 1 that was used for this practised example consisted of 7 wt % Si, 0.5 wt % Fe, 0.2 wt % Cu, 0.4 wt % Mg, 0.5 wt % Zn and a remainder of Al and less than 0.01 wt % unavoidable impurities. Precipitation nuclei 2 used in this practised example included TiC.

The temperature of the molten aluminium alloy was 720° C. An amount of the precipitation nuclei 2 added into the molten aluminium alloy 1 was one tenth of the mass of the molten aluminium alloy. The temperature of the precipitation nuclei 2 was 500° C. when they were added.

<Temperature Keeping Process>

As is shown in FIG. 1A, the molten aluminium alloy 1 was gradually cooled to 590° C. in the temperature keeping process of the production method of this practised example 1. Initially precipitated nuclei 3 nucleated in the molten aluminium alloy 3 while the temperature of the molten aluminium alloy 1 was lowering. Accordingly the molten aluminium alloy 1 contains a high density of the nuclei including the precipitation nuclei 2 that are separated into the molten aluminium alloy 1 (Liquid phase L) from the solid phase S and the initially precipitated nuclei 3 that nucleated from the liquid phase L of the molten aluminium alloy.

In the production method of this practised example, the nucleation as above explained took place when the molten aluminium alloy was kept at the predetermined keeping temperature for the predetermined keeping time.

In the production method of this practised example, the predetermined keeping time was 590° C. and the predetermined keeping time [sec] was 20˜90 [sec].

<Casting Process>

Next, a casting process of casting the molten aluminium alloy 1 after the temperature keeping process as indicated in FIG. 1A into a metal mold (not shown) was carried out.

Intermetallic compounds precipitated and grew larger from nuclei (added precipitation nuclei 2 and initially precipitated nuclei 3) increased in the molten aluminium alloy in the metal mold. When the precipitation and the growth got started, intermetallic compounds 4 almost simultaneously precipitate on the increased nuclei in the molten aluminium alloy. As a result, the aluminium alloy 5 obtained after the molten aluminium alloy 1 solidified contained fine intermetallic compounds 4. Furthermore, since nuclei that nucleate during the temperature keeping process have a smaller size, the intermetallic compounds 4 in the aluminium alloy 5 are certainly made fine. The intermetallic compounds 4 in the aluminium alloy 5 obtained through the temperature keeping process are 11% smaller than those in the aluminium alloy 5 without having gone through the temperature keeping process.

COMPARISON EXAMPLE

As is shown in FIG. 1B, the molten aluminium alloy 1 used for the production method of the comparison example did not contain precipitation nuclei 2 of a Solid phase S before being cooled, which differed from the present embodiment. Then, when the molten aluminium alloy 1 was cooled to the predetermined temperature, precipitation nuclei 3 nucleated in the molten aluminium alloy 1. Then when the molten aluminium alloy was further cooled, the molten aluminium alloy 1 solidified to be the aluminium alloy 5 with intermetallic compounds having precipitated on the precipitation nuclei 3 and grown larger to be coarse intermetallic compounds. 

1. A production method for aluminium alloys comprising; an addition process of adding into a molten aluminium alloy a precipitation nucleus on which an intermetallic compound is capable of precipitating when the molten aluminium alloy is solidifying and a casting process of casting the molten aluminium alloy containing the precipitation nucleus into a metal mold.
 2. The production method for aluminium alloys as described in claim 1 further comprising a temperature keeping process of keeping the molten aluminium alloy containing the precipitation nucleus at a predetermined temperature for a predetermined time, the temperature keeping process to be carried out between the addition process and the casting process.
 3. The production method for aluminium alloys as described in claim 1 wherein adding Be and Mn in addition to the precipitation nucleus into the molten aluminium alloy containing Fe.
 4. The production method for aluminium alloys as described in claim 1 wherein the precipitation nucleus has a disregistry factor δ defined by a following equation that is equal to or lower than 10%. δ_((hkl)n) ^((hkl)s)=1/3Σ_(i=1) ³ |d[uvw]_(s) ^(i) cos θ−d[uvw]_(n) ^(i) |/d[uvw]_(n) ^(i)×100 [%] where, (hkl)_(s) refers to a low-order index face of a different nucleus particle, [uvw]_(s) refers to a low-order index direction of the (hkl)_(s) face, (hkl)_(n) refers to a low-order degree index face of a metal whose nuclei are generated, [uvw]_(n) refers to a low-order index direction of the (hkl)_(n) face, d [uvw]_(s) refers to a distance between atoms in the [uvw]s direction, d [uvw]_(n) refers to a distance between atoms in the [uvw]_(n) direction, and θ refers to a angle between [uvw]_(s) and [uvw]_(n).
 5. The production method for aluminium alloys as described in claim 1 wherein the precipitation nucleus is
 6. The production method for aluminium alloys as described in claim 1 wherein the precipitation nucleus consists of an AlFeSi system intermetallic compound.
 7. The production method for aluminium alloys as described in claim 1 wherein the precipitation nucleus consists of TiC. 